If you have the YS63 you should take advantage of its pessurized fuel system and mount the tank as far back as possible, to the front servo tray bulkhead, so it's close to the CG. You will have to cut a hole in cockpit floor and the angled bulkhead to clear the tank though.

You don't absolutely need an aluminum spinner as I know people who run plastic ones safely on 4-strokes but I would not take the risk myself. Plus plastic spinners are hard to align and mount because you have to match everything to the spinner's screwholes or plastic locking tabs- and you have to do it every time you change props. So I would reccomend an aluminum spinner.

I would just run the antenna inside the fuselage in a plastic tube. I only recently started doing this and have had no trouble with it.